(a) Field of the Invention
The present invention relates to an image-transmitting optical system and, more particularly to an image-transmitting optical system for endoscopes (which are not flexible) in which an image of an object is transmitted in turn by using a plural number of relay lenses.
(B) Description of the Prior Art
An image focused after passing through a plural number of relay lenses for image transmission as shown in FIG. 1 generally causes considerable negative astigmatism and curvature of field. When one of said plural number of relay lenses is taken up, negative astigmatism caused by that lens is shown in FIG. 2 and curvature of field caused by the same lens is shown in FIG. 3. When, therefore, the number of relay lenses becomes larger, negative astigmatism also becomes larger. This tendency becomes more conspicuous when the focal length of relay lenses is shorter. Curvature of field also increases when the number of relay lenses used for image transmission becomes larger and, consequently, flatness of the image becomes more unfavourable.
Besides, for an image-transmitting optical system, it is desirable that deterioration of the image caused by aberrations is minimized and intensity of transmitted light is maximized.